Exergy Analysis of Metal Oxide Carbothemic Reduction under Vacuum –

Based on the fundamental Le Chatellier principle, gas producing reactions can be pushed at lower temperatures if an appropriate vacuum is applied. A basic thermodynamic analysis is used to predict the effect of pressure decrease on the temperature and exergy cost of a reaction with gaseous products. The energy analysis of 11 different metal producing carbothermic reductions revealed that the pumping work substitutes relatively the same amount of heat in all 11 reactions, despite the fact that the volume of gases evolved in each case differs significantly. The exergy analysis for conducting these reactions with non-renewable resources showed that due to the high exergy cost of fossil fuel generated electricity the application of vacuum would increase the overall exergy cost of these reductions. If the heat needed for the reactions could be produced through renewable resources, such as concentrated solar radiation, then the use of vacuum would have a positive effect in the cases of high temperature reductions of Al2O3, MgO and CaO, where a significant decrease in reaction temperature is observed as more exergy is spent in pumping work